Citi Research lowered its rating on Corning to neutral from buy, saying the glass and specialty materials maker is fully valued after a significant increase in its share price.
The company's Gorilla glass product is used in Apple iPhone displays. Corning shares are up 32 percent in the last 12 months through Thursday.
"Investors are keenly focused on the iPhone 8 'supercycle' as it pertains to Corning but we believe this is well reflected in estimates," analyst Stanley Kovler wrote in a note to clients Friday. "Prospects for late 2018 LCD industry capacity additions, tougher comps for 2H smartphone trends next year and limited gross margin upside from mix shift to fast growing but below corp avg. margin optical business also implies minimal upside potential to our 2018 EPS."